1. Field of the Invention
The present invention relates to a resinoid bonded grinding wheel and method for forming the same which has hard abrasives, such as diamond or cubic boron nitride, bonded on a support member which is made of porous ceramics, such as, for example, a vitrified grinding wheel.
2. Description of the Prior Art
A prior resinoid bonded grinding wheel is known which is provided with a support member to which is affixed grinding element including a diamond or cubic boron nitride abrasives distributed in a bonding matrix. In general, since the support member is made of a metallic material, such as aluminum-base alloy, which has a relatively high thermal conductivity and a high coefficient of thermal expansion, the grinding wheel is caused to expand by heat transmitted from bearing members and the grinding area between the grinding element and a workpiece, thereby resulting in inaccurate grinding.
In order to solve these disadvantages, it has been considered to utilize a resinoid bonded grinding wheel having a support member which is made of porous ceramics such as a vitrified grinding wheel which contains alumina or silicon carbide abrasives bonded by a vitrified bonding matrix. The thermal conductivity and the coefficient of thermal expansion of the vitrified grinding wheel are advantageously so low that it is effective in preventing the resulting heat during use from being transmitted to the entire body of the support member and to avoid thermal expansion of the support member. However, since the support member is porous and the grinding element affixed thereto is impervious to water, a liquid lubricant or coolant penetrates into the support member. Such penetration may cause a weight imbalance of the grinding wheel. Particularly, in the case of a grinding wheel having two conical grinding surfaces on the outer periphery thereof as shown in FIG. 2, the coolant penetrates into the support member and is accummulated in the inside corner between the two conical grinding surfaces during rotation of the support member, because it cannot be discharged through the grinding element.
When the grinding wheel is rotating, weight imbalance thereof does not occur. However, when rotation of the grinding wheel is discontinued, the coolant which has penetrated into the support member starts to flow downwardly due to the effect of gravity and is accumulated in the bottom part of the support member to thereby cause weight imbalance of the grinding wheel. Therefore, when the rotation of the grinding wheel is restarted, the weight imbalance generates a corresponding vibration during the grinding operation, thereby causing inaccurate grinding results. Furthermore, even in the situation where a straight-type grinding wheel is utilized which has a cylindical grinding surface, weight imbalance of the grinding wheel may occur because the coolant cannot be discharged through the grinding element thereof.